1. Field of the Invention
The present invention relates to thin film structures in which a conductive protrusion is provided on a conductive layer and is surrounded by an insulating layer formed on the conductive layer, and more particularly, relates to a thin film structure having resistance against mechanical impact or the like and a manufacturing method thereof.
2. Description of the Related Art
FIG. 40 is a cross-sectional view of a related thin film structure. In this thin film structure, for example, a conductive layer 2 is formed on an insulating layer 1, the conductive layer 2 being connected to a lead layer extending from a coil layer of an inductive magnetic head or to a lead layer extending from an electrode layer of a magnetoresistive effect element. On the conductive layer 2, a protrusion (bump) 4 is formed with a metal film 3 interposed therebetween. Around the protrusion (bump) 4, an insulating layer 5 made of Al2O3 or SiO2 is formed, and the upper surface of the protrusion (bump) 4 is exposed at the surface of the insulating layer 5. The metal layer 3 is a remaining part of a current-carrying layer which was used for supplying current for forming the protrusion 4 by plating.
The protrusion 4 has a base portion 4a connected to the metal film 3 and an upper portion 4b provided on this base portion 4a. A sidewall part of the upper portion 4b extends outward from a periphery of the base portion 4a to form an extending part 4c. On the upper surface of the protrusion 4, a metal pad 6 made of a metal material is formed.
FIGS. 41 to 45 are cross-sectional views for illustrating a manufacturing method of the related thin film structure.
First, in a step shown in FIG. 41, the conductive layer 2 is formed on the insulating layer 1 by plating. Next, over the conductive layer 2 to the insulating layer 1, a current-carrying layer 7 used for forming the protrusion 4 by plating is formed by sputtering. In addition, on the current-carrying layer 7, a resist layer R for forming the bump is provided, and an opening portion Ra is formed in the resist layer R at a position at which the protrusion 4 is to be formed. In this method, the current-carrying layer 7 is formed to extend in the right direction in the figure, and from an end portion thereof, current is to be supplied.
Next, in a step shown in FIG. 42, on the current-carrying layer 7 exposed through the opening portion Ra of the resist layer R, isotropic plating is performed using nickel (Ni), gold (Au), copper (Cu), or a conductive material containing Cu, thereby forming the protrusion 4. For example, a height H1 of the protrusion 4 is 40 μm.
After the protrusion 4 is formed, the resist layer R is removed, and as a result, the state shown in FIG. 43 can be obtained. Next, the current-carrying layer 7 around the protrusion 4 is removed by ion milling or the like. In this milling, a part of the current-carrying layer 7 located under the upper portion 4b of the protrusion 4 remains, and as a result, the metal film 3 shown in FIG. 44 is formed.
After the current-carrying layer 7 is removed, as shown in FIG. 45, on the conductive layer 2 and the protrusion 4, the insulating layer 5 is formed which is made of Al2O3 or SiO2.
Next, in order to expose the protrusion 4 at the surface of the insulating layer 5, the insulating layer 5 is milled, for example, to a level indicated by the line A-A shown in the figure, and the metal pad 6 is then formed, thereby forming the thin film structure shown in FIG. 40.
In addition, in Japanese Unexamined Patent Application Publication No. 4-21919, a technique has been disclosed in which a wire density can be increased by disposing another lead conductor 28 under the protrusion 4. The thin film structures and the manufacturing methods thereof as described above have been disclosed in the following six patent documents, that is, Japanese Unexamined Patent Application Publication Nos. 11-100690 (p. 3, FIG. 1), 9-73608 (p. 3, FIG. 3), 2000-149221 (p. 3, FIG. 8), 58-179922 (pp. 1 and 2, FIGS. 2 and 3), 4-21919 (pp. 4 and 5, FIGS. 5 and 6), and 2003-123208 (pp. 4 and 5, FIGS. 1 to 8).
However, the related thin film structure described above has the following problems.
In the step shown in FIG. 43, when the resist layer R is removed, a space S is formed under the extending part 4c of the upper portion 4b of the protrusion 4. When the insulating layer 5 is formed in the step shown in FIG. 45, since the space S is present under the extending part 4c, the insulating layer 5 is not filled in the space S, and hence a void is formed. As described above, when the space S under the extending part 4c of the protrusion 4 remains as the void, the mechanical strength of the insulating layer 5 is decreased, and as a result, in the milling step shown in FIG. 45, a crack C indicated by a dotted line is liable to be formed in the insulating layer 5. When the crack C is formed in the insulating layer 5, corrosion resistance of the thin film structure is extremely degraded, and in addition, wire-breakage may occur in some cases.
In addition, in Japanese Unexamined Patent Application Publication No. 58-179922, the structure has been disclosed in which an overhang part (extending part) of a conductor (protrusion) is removed by milling (milling along chain lines E shown in FIG. 44) so that the space formed under the overhang part is eliminated, and in which an insulating layer is formed around the entire periphery of the conductor (protrusion). However, since the step of milling the conductor (protrusion) is additionally performed, the manufacturing process becomes complicated, and in addition, due to the decrease in volume of the conductor (protrusion), a problem may arise in that the electrical resistance is increased. Furthermore, the variation in volume of the conductor (protrusion) is increased, and as a result, the electrical resistance also varies.
In addition, according to the thin film structure disclosed in Japanese Unexamined Patent Application Publication No. 2063-123208, it is difficult to supply current for forming a lower pad 3A and an upper pad 3B by plating, and hence the structure described above must be further improved.